Keeping Tabs on Comet ISON

The interloper visits Spica and Mercury

By J. Alex Knoll

Mercury is putting on its best pre-dawn show of 2013, more than doubling in brightness this week, from +1 magnitude to –0.5 (each order of magnitude is exponential, so an increase from +1 to 0 is a doubling). Monday marks the innermost planet’s greatest elongation — its farthest point away from the sun as seen from earth and its highest point above the horizon. Mercury rises a little before 6am and climbs nearly 15 degrees above the southeast horizon before the sun rises more than an hour later. Ten degrees above Mercury is blue-white Spica, but even this first-magnitude star pales compared to Mercury this week.
First discovered last September, Comet ISON is heading into the inner solar system for the first time, coming within 700,000 miles of the sun November 27. If the comet survives that close encounter, it could live up to the comet of the century billing. If not, the next two weeks are your best chance to spot this long-distance traveler.
With binoculars or a small telescope, look for ISON one degree to the west of Spica Sunday before dawn and less than one-half degree to the east of the star the next morning. By next Thursday and Friday, ISON will be within 10 degrees of Mercury — well within your binoculars’ field of view. Perhaps by then it will be bright enough to see with the unaided eye.
Sunday marks the full moon, the Beaver Moon and the Frost Moon according to lore. The full moon floats just six degrees below the miniature dipper-shape of the Pleiades star cluster, while Monday night it is even closer to Aldebaran, the red eye of Taurus the bull. The full moon’s glow washes out all but the brightest meteors in this year’s Leonid shower, which peaks between the 16th and 18th. Still, the Leonids are active through the month, so patience or luck will likely reward you with a few of these shooting stars.